This trial will be conducted in Africa, Asia, North America and South America. The aim of this clinical trial is to compare NN1250 (insulin degludec) with sitagliptin, as add-on to subject's own current oral antidiabetic (OAD) treatment, in subjects with type 2 diabetes inadequately controlled with 1-2 OADs (metformin, sulphonylurea, glinides or pioglitazone).

Ongoing treatment with 1 or 2 of the following OADs (metformin, insulin secretagogue (sulphonylurea or glinides) or pioglitazone) in any combination with unchanged dosing for at least 3 months prior to Visit 1 with the minimum doses stated: -Metformin: alone or in combination (including fixed combination)1500 mg or maximum tolerated dose (at least 1000 mg daily) -Insulin secretagogue (sulfonylurea or glinide): minimum half of the maximal daily dose according to local labelling -Pioglitazone: minimum half of the maximal daily dose according to local labelling or maximum tolerated dose

Body Mass Index (BMI) below or equal to 40.0 kg/m^2

HbA1c 7.5-11.0 % (both inclusive) by central laboratory analysis

Exclusion Criteria:

Use within the last 3 months prior to Visit 1 of: exenatide, liraglutide, rosiglitazone or acarbose

Recurrent severe hypoglycaemia (more than 1 severe hypoglycaemic event during the last 12 months) or hypoglycaemic unawareness as judged by the Investigator or hospitalisation for diabetic ketoacidosis during the previous 6 months

Pregnancy, breast-feeding, the intention of becoming pregnant or not using adequate